System and Method for Low Latency Wireless Connection

ABSTRACT

A method of establishing a low latency connection between a first device and a second device on a wireless network is presented. The method contains the steps of: forming a first wireless connection between the first and second devices; forming at least a second and parallel wireless connection between the first and second devices; and sending data between the first and second devices using at least the first and second connections. For any wireless protocol for data exchange between devices that specifies a minimum interval between data exchange events, the present disclosure enables a lower latency than would otherwise be achievable according to a standard protocol.

TECHNICAL FIELD

The present disclosure relates to establishing a low latency wirelessconnection between two devices. In particular, but not exclusively, thepresent disclosure relates to establishing a low latency Bluetooth LowEnergy (BLE) connection between two devices.

BACKGROUND

There are many practical applications involving a wireless network whereit is desirable to have the lowest connection latency possible.Connection Latency is defined as the time taken for the transport ofdata from one device to another. One example of where low connectionlatency is required is within a gaming context where a handheldcontroller is wirelessly connected to a main console unit. Suchapplications typically require an overall latency of the wirelessconnection to be 5 ms or less. If the latency is greater, the user maynotice the delay between pressing a command button on the controller andthe response within the game. Another example where low latency isimportant is a virtual reality (VR) system with a wirelessly connectedVR headset. Typically, game console and VR system providers usespecialised firmware, hardware and/or software for establishing a lowlatency connection.

One popular protocol for wireless connectivity is Bluetooth. A recentversion of this is the Bluetooth Low Energy (BLE) standard, alsoreferred to as Bluetooth Smart. Its operation is defined by variousstandards and specifications which are managed by the Bluetooth SpecialInterest Group. Given the ubiquitous nature of Bluetooth connectivity,it is desirable that low latency connection can be established using theBluetooth or BLE protocol.

However, the BLE specification defines a connection model for BLE with aminimum connection interval of 7.5 ms. The purpose of this minimumconnection interval is to save power, which is a key objective of theBLE standard. The advantage of having a relatively long connectioninterval is that significant power is saved, since a device can sleepmost of the time between connection events. The disadvantage is that ifa device has data that it needs to send, it must wait until the nextconnection event. A shorter connection interval provides moreopportunity for data to be sent or received, as the two devices willconnect more frequently.

Under the BLE standard (low power method), and using the minimumconnection interval, two devices cannot connect and exchange data morefrequently than every 7.5 ms. For a high power solution, the BLEspecification defines a method that enables both connected devices tocontinue sending and receiving (using the More Data bit) but this is notpractical for a battery operated handheld device. For applications suchas gaming, the amount of data that needs to be sent (the payload) istypically small, such as a handheld controller transmitting datarepresenting the pressing of a command button or movement of the VRhandheld unit.

The BLE standard defines two device roles at the Link Layer for aconnection: the master device and the slave device. These are thedevices that act as initiator and advertiser respectively duringcreation of the connection. A master device can manage multiplesimultaneous connections with different slave devices, whereas eachslave device can only be connected to one master device. Thus, a networkcan be formed which comprises a master device and multiple slavedevices, and this is called a piconet.

Within the network, each slave device has its own unique media accesscontrol address (MAC address). This is a device identifier assigned tonetwork interfaces for communications at the data link layer of anetwork segment. It is possible to change the MAC address on most modernhardware and many network interfaces (including wireless ones) supportchanging their MAC address.

SUMMARY

According to a first aspect of the present disclosure there is provideda method of establishing a low latency wireless connection between afirst device and a second device, the method comprising the steps of:forming a first wireless connection between the first and seconddevices; forming at least a second and parallel wireless connectionbetween the first and second devices; and sending data between the firstand second devices using at least the first and second connections.

Optionally, the wireless connection is established on a BLE network.

Optionally, the method includes offsetting the start time of successiveconnection events by an offset time period.

Optionally, the offset time period between consecutive connectionintervals is substantially equal to the ratio of the connection intervaland the number of wireless connections.

Optionally, the offset time period between consecutive connectionintervals is around 0.5 ms.

Optionally, the first device comprises a master device and the seconddevice comprises a slave device, and wherein the slave device has afirst device identifier.

Optionally, the first device identifier comprises a first MAC address.

Optionally, the slave device adopts a second device identifier afterforming of the first wireless connection and prior to forming of thesecond wireless connection.

Optionally, the slave device adopts a new device identifier for eachwireless connection.

Optionally, the master device combines the data sent using a pluralityor all of the parallel wireless connections, and processes the combineddata.

According to a second aspect of the present disclosure there is provideda system of wirelessly connected devices, the system comprising: a firstdevice and a second device; wherein the system is configured to providea first wireless connection between the first and second devices and toprovide at least a second and parallel wireless connection between thefirst and second devices, and wherein data is sendable between the firstand second devices using at least the first and second wirelessconnections.

Optionally, the system is configured to wirelessly connect the first andsecond devices using a BLE network.

Optionally, the system is configured to offset a start time ofsuccessive connection events by an offset time period.

Optionally, the offset period between consecutive connection intervalsis substantially equal to the ratio of the connection interval and thenumber of wireless connections.

Optionally, the first device comprises a master device and the seconddevice comprises a slave device, and wherein the slave device has afirst device identifier.

Optionally, the first device identifier comprises a first MAC address.

Optionally, the system is configured to specify a second deviceidentifier for the slave device prior to forming the second wirelessconnection.

Optionally, the system includes a multiplexer for combining the datasent using a plurality or all of the parallel wireless connections.

According to a third aspect of the present disclosure there is provideda master device which is wirelessly connectable to a slave device, themaster device comprising: a radio transceiver which is configured toprovide a first wireless connection between the master device and slavedevice, wherein the radio transceiver is configured to provide a secondand parallel wireless connection between the master device and the slavedevice, and wherein data is sendable between the master device and theslave device using at least the first and second wireless connections.

According to a fourth aspect of the present disclosure there is provideda slave device which is wirelessly connectable to a master device, theslave device comprising: a radio transceiver which is configured toprovide a first wireless connection between the master device and slavedevice, wherein the radio transceiver is configured to provide a secondand parallel wireless connection between the master device and the slavedevice, and wherein data is sendable between the master device and theslave device using at least the first and second wireless connections.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be described below, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic view of a system comprising two wirelesslyconnected devices; and

FIG. 2 is a timeline diagram showing the timing of connection events forthe devices of FIG. 1.

DESCRIPTION

BLE is defined in various standards documents, including for example the“Specification of the Bluetooth System”, Covered Core Package version4.2, Volumes 1-7, which are hereby incorporated by reference.

FIG. 1 shows a system 10 comprising two devices which are wirelesslyconnected via a BLE network. Bluetooth enabled devices are “peer units”in that they are able to act as either a master or a slave device.However, when a piconet is formed between two or more devices, onedevice takes the role of ‘master’, and all other devices assume a‘slave’ role. In FIG. 1, a first device is acting as the master device20 while a second device is acting as the slave device 30.

According to the BLE standard, the master device 20 determines the timeinstants in which the slave device 30 is required to listen, and thuscoordinates the medium access by using a Time Division Multiple Access(TDMA) scheme. The master device 20 also provides the slave device 30with the information needed for frequency hopping when transmitting dataand for the connection supervision. The parameters for the management ofa connection are transmitted in a Connection Request message.

Once a connection between the master and slave devices has been created,data channel protocol data units (PDUs) are exchanged during the courseof a connection event. Connection events occur at regular time intervalsspaced by a time period called a connection interval. During aconnection event, at least an Inter Frame Space (IFS) of 150 μs mustpass between the end of the transmission of a data PDU and the start ofthe next one. If none of the devices has more data to transmit, theconnection event will be closed and the slave device 30 will not berequired to listen until the beginning of the next connection event. Fora new connection event, master and slave devices use a new data channelfrequency, which is computed using the frequency hopping algorithm.

Therefore, the Link Layer only transmits data during connection events.During a connection event, the master and slave devices alternatesending and receiving data packets. To aid clarity, only data sent fromthe slave device 30 to the master device 20 is considered and describedin the present disclosure.

The master device 20 includes an RF transceiver 22 for wirelesslytransmitting and receiving data. The master device 20 could be, forexample, a main console of a gaming system. The slave device 30 alsoincludes an RF transceiver 32 for wirelessly transmitting and receivingdata. The slave device 30 may be, for example, a handheld controller ofthe gaming system.

The RF transceivers and software installed on both the master device 20and the slave device 30 are used to form a first wireless connection 40between the devices. Indeed, the system 10 is configured to formmultiple parallel wireless connections between the two devices, and datais sent between the devices using all of the formed wirelessconnections.

In the present embodiment, fifteen parallel connections between themaster device 20 and the slave device 30 are formed (in FIG. 1, only thefirst and fifteenth wireless connections 40, 42 are shown for clarity).

Multiple connections between a master and a slave device are achievedusing the following.

As is conventional, the slave device 30 has a first device identifier inthe form of a first MAC address. The first wireless connection 40 isformed between the two devices according to the standard BLE protocolwith the slave device 30 using this MAC address. As part of theconnection procedure, a first connection interval 50 is specified by themaster device 20. The connection interval may be in the range of 7.5 msto 4.0 s. In this embodiment, it is set to the minimum possible timeperiod of 7.5 ms.

After forming the first connection 40, the slave device 30 adopts a new,second MAC address. The master and slave devices 20, 30 then connectagain to form a second wireless connection. As before, a connectioninterval of 7.5 ms is set by the master device 20 for the secondwireless connection.

Effectively, the master device 20 acts conventionally when making thesecond connection, as if it were connecting to a second device (such asa second handheld controller). No changes are required to the Bluetoothhardware and software stack in the master device 20.

The slave device 30 also does not require any physical modification. Allnecessary modifications can be implemented at the link layer.

The master device 20 and slave device 30 continue to make newconnections, with the slave device 30 adopting a new MAC address priorto making each wireless connection. For each connection, a connectioninterval of 7.5 ms is set by the master device 20.

As part of the connection procedure, the master device 20 offsets thestart time 62 of the second connection event (for the second wirelessconnection) relative to the start time 52 of the first connection event50 (for the first wireless connection). This is shown in FIG. 2. This isin a similar manner to the conventional situation in which the masterdevice 20 is scheduling the timing for the transmission of data frommultiple slave devices. The master device 20 offsets the start time ofeach subsequent connection event by the same time period. When all ofthe wireless connections have been made, the timing of the connectionevents associated with each of the wireless connections is staggered asshown in FIG. 2, with an offset time period between each successiveconnection event.

For cases where a connection interval is the same for each of theplurality of parallel connections, the offset time period between thestart points of successive connection intervals is determined from theratio of the connection interval and the number of wireless connections.Thus, for the present embodiment which uses a connection interval of 7.5ms and 15 connections, the offset time period is 0.5 ms. As statedabove, in a gaming context a handheld controller typically only needs totransmit a small data payload to represent a button press or other eventand so 0.5 ms is quite sufficient for sending the data.

In operation, when a user presses a command button of the slave device30, the data 54 representing the button press is stored in a buffer ofthe slave device 30 until the next available connection event. If thebutton is pressed, say, at or just before start time 52 of a firstconnection event, the data 54 will be sent using the first wirelessconnection 40. If the button is pressed between the start time 52 of thefirst connection event and the start time 62 of the second connectionevent, the data 54 will be sent using the second wireless connection. Asimilar approach is used for later times in that any waiting data 54 issent after the next available connection event, regardless of whichwireless connection is used. This next available connection event willalways be within the next 0.5 ms from when the button press is detected.Therefore, the maximum time between the button press and the sending ofthe data 54 representing the button press will be the offset timeperiod. The offset time period therefore represents the maximumconnection latency that will be experienced, which in the presentembodiment is 0.5 ms.

Consider the conventional case where a single slave device 30 isconnected to a master device 20 using a 7.5 ms connection interval. If auser presses a command button of the slave device 30 just after theconnection event for the slave device 30, the data 54 representing thebutton press will be stored in a buffer of the slave device 30 until thenext connection event which takes place in the next connection interval.Therefore, there will be a delay of nearly 7.5 ms (plus additionalprocessing delay in software) before the master device 20 reconnects tothe slave device 30 and the data 54 is transmitted. The user may noticesuch a delay.

Returning to the disclosure, the master device 20 includes a multiplexer70 (shown in FIG. 1) which receives the data 54 sent using all of theparallel wireless connections and presents it to a host as beingassociated with a single slave device. The master device 20 thenprocesses the data. Therefore, a single physical device can in effectmasquerade as several devices with multiple parallel connections, sothat a lower effective latency can be achieved as compared with theminimum latency associated with a protocol for wireless data exchange.

The present embodiment establishes fifteen wireless connections and usesthe minimum connection interval possible under the BLE standard. Inother embodiments, fewer wireless connections or more wirelessconnections can be made. A greater number of connections decreases theoffset time period and therefore provides an even smaller connectionlatency. A lesser number of connections increases the offset time periodand therefore also increases the connection latency but this could beuseful when greater payloads are to be transmitted. Similarly, using aconnection interval greater than the minimum possible increases theconnection latency but allows the transmittal of greater payloads. Thereis also a saving in the power consumed. The number of wirelessconnections and the choice of connection interval can be optimised forthe particular requirements of the application involved.

As a further variation, the connection interval does not have to be thesame for all of the parallel connections which are established.

The present disclosure overcomes a limitation of the Bluetooth standardto provide low latency connection over a Bluetooth network. The approachof the disclosure is low power, flexible and can be optimised for aparticular application. The invention is within the BT-SIG qualificationprocess and does not violate Bluetooth specification and testing.

The disclosure is relatively straightforward to implement and does notrequire any physical modification of the slave device 30. The onlyphysical modification to the master device 20 is the use of amultiplexer 70. The modifications to the master device 20 and the slavedevice 30 can be made using firmware updates. Similarly, for anywireless protocol for data exchange between devices that specifies aminimum interval between data exchange events, the present disclosureenables a lower latency than would otherwise be achievable according toa standard protocol. Examples of other wireless protocols include ZigBeeLPWAN, and other Bluetooth versions both past and future.

Various modifications and improvements can be made to the above withoutdeparting from the scope of the disclosure.

What is claimed is:
 1. A method of establishing a low latency wirelessconnection between a first device and a second device, the methodcomprising the steps of: forming a first wireless connection between thefirst and second devices; forming at least a second and parallelwireless connection between the first and second devices; and sendingdata between the first and second devices using at least the first andsecond connections.
 2. The method as claimed in claim 1, wherein thewireless connection is established on a BLE network.
 3. The method asclaimed in claim 1, including offsetting the start time of successiveconnection events by an offset time period.
 4. The method as claimed inclaim 3, wherein the offset time period between consecutive connectionintervals is substantially equal to the ratio of the connection intervaland the number of wireless connections.
 5. The method as claimed inclaim 3, wherein the offset time period between consecutive connectionintervals is around 0.5 ms.
 6. The method as claimed in claim 1, whereinthe first device comprises a master device and the second devicecomprises a slave device, and wherein the slave device has a firstdevice identifier.
 7. The method as claimed in claim 6, wherein thefirst device identifier comprises a first MAC address.
 8. The method asclaimed in claim 6, wherein the slave device adopts a second deviceidentifier after forming of the first wireless connection and prior toforming of the second wireless connection.
 9. The method as claimed inclaim 6, wherein the slave device adopts a new device identifier foreach wireless connection.
 10. The method as claimed in claim 6, where inthe master device combines the data sent using a plurality or all of theparallel wireless connections, and processes the combined data.
 11. Asystem of wirelessly connected devices, the system comprising: a firstdevice and a second device; wherein the system is configured to providea first wireless connection between the first and second devices and toprovide at least a second and parallel wireless connection between thefirst and second devices, and wherein data is sendable between the firstand second devices using at least the first and second wirelessconnections.
 12. The system as claimed in claim 11, wherein the systemis configured to wirelessly connect the first and second devices using aBLE network.
 13. The system as claimed in claim 11, wherein the systemis configured to offset a start time of successive connection events byan offset time period.
 14. The system as claimed in claim 13, whereinthe offset period between consecutive connection intervals issubstantially equal to the ratio of the connection interval and thenumber of wireless connections.
 15. The system as claimed in claim 11,wherein the first device comprises a master device and the second devicecomprises a slave device, and wherein the slave device has a firstdevice identifier.
 16. The system as claimed in claim 15, wherein thefirst device identifier comprises a first MAC address.
 17. The system asclaimed in claim 15, wherein the system is configured to specify asecond device identifier for the slave device prior to forming thesecond wireless connection.
 18. The system as claimed in claim 11,including a multiplexer for combining the data sent using a plurality orall of the parallel wireless connections.
 19. A master device which iswirelessly connectable to a slave device, the master device comprising:a radio transceiver which is configured to provide a first wirelessconnection between the master device and slave device, wherein the radiotransceiver is configured to provide a second and parallel wirelessconnection between the master device and the slave device, and whereindata is sendable between the master device and the slave device using atleast the first and second wireless connections.
 20. A slave devicewhich is wirelessly connectable to a master device, the slave devicecomprising: a radio transceiver which is configured to provide a firstwireless connection between the master device and slave device, whereinthe radio transceiver is configured to provide a second and parallelwireless connection between the master device and the slave device, andwherein data is sendable between the master device and the slave deviceusing at least the first and second wireless connections.
 21. The systemas claimed in claim 13, wherein the offset time period betweenconsecutive connection intervals is around 0.5 ms.
 22. The system asclaimed in claim 15, wherein the slave device adopts a new deviceidentifier for each wireless connection.